This invention relates to electric hammers, in particular hammers having an air cushion hammering mechanism.
Such hammers will normally have a housing and a hollow cylindrical spindle mounted in the housing. The spindle allows insertion of the shank of a tool or bit, for example a drill bit or a chisel bit, into the front end thereof so that it is retained in the front end of the spindle with a degree of axial movement. The spindle may be a single cylindrical part or may be made of two or more co-axial cylindrical parts, which together form the hammer spindle. For example, a front part of the spindle may be formed as a separate tool holder body for retaining the tool or bit. Such hammers are provided with an impact mechanism which converts the rotational drive from an electric motor to a reciprocating drive causing a piston, which may be a hollow piston, to reciprocate within the spindle. The piston reciprocatingly drives a ram by means of a closed air cushion located between the piston and the ram. The impacts from the ram are transmitted to the tool or bit of the hammer, optionally via a beatpiece.
Such hammers can also be employed in combination impact and drilling mode or in a drilling only mode in which the spindle, or a forwardmost part of the spindle, and hence the bit inserted therein will be caused to rotate. In the combination impact and drilling mode the bit will be caused to rotate at the same time as the bit receives repeated impacts. A rotary drive mechanism transmits rotary drive from the electric motor to the spindle to cause the spindle, or a forwardmost part thereof to rotate.
In smaller hammers, a wobble drive arrangement is generally used to convert a rotary drive from the motor to the reciprocating drive of the piston. In a known arrangement the rotary drive from the motor is transmitted to an intermediate shaft mounted within the hammer housing generally parallel to the axis of the spindle. A wobble sleeve is rotatably mounted on the intermediate shaft. The wobble sleeve is formed with a wobble race which extends around the wobble sleeve at an oblique angle to the axis of the intermediate shaft. Balls are set to run between this inner race and an outer race formed on a wobble ring, which wobble ring has a wobble pin extending from it to the rearward end of the piston. The inner race, outer race and the balls running between the races together form a wobble bearing. The wobble pin is pivotally connected to the rearward end of the piston via a trunnion arrangement. Thus, when the wobble sleeve is rotatably driven the wobble pin reciprocates and reciprocatingly drives the piston within the spindle and hammering occurs. In drilling only mode hammering is not required and so a mode change mechanism is required to selectively transmit the rotation of the intermediate shaft to the wobble sleeve.
In DE35,03,507, U.S. Pat. No. 5,373,905 and EP403,789 intermediate shaft and wobble plate sub-assemblies are shown in which the rearward support bearing for the intermediate shaft is mounted around the wobble sleeve, using the wobble sleeve to form the inner race of the wobble bearing. This has the effect of reducing the number of components, but results in a relatively long combined length for the intermediate shaft and spindle and so is not compact.
In smaller hammers, where the compactness of the hammer is a critical design issue, the intermediate shaft and wobble plate sub-assembly must be compact as well as being robust enough to operate reliably in the high vibration environment of a hammer.
The present invention aims to provide a rotary hammer arrangement with a compact and robust intermediate shaft and wobble sleeve sub-assembly.
Hammer Comprising:
a tool holder located at a forward end of the hammer;
a hammering mechanism for generating repeated impacts on a tool or bit mounted in the tool holder;
a rotatably driven intermediate shaft; and
a wobble drive arrangement for reciprocatingly driving the hammering mechanism, which wobble drive arrangement includes a wobble sleeve mounted on the intermediate shaft and a wobble bearing mounted on the wobble sleeve;
characterised in that a support bearing for the intermediate shaft is mounted on the wobble sleeve forwardly of the wobble bearing.
The location of the support bearing nearer to the forward end of the wobble sleeve enables a compact design of intermediate shaft and wobble drive arrangement sub-assembly design with a significant overlap between the axial length of the intermediate shaft and of the spindle. This is partly enabled because the wobble bearing, and thus the wobble drive arrangement may be located further towards the rearward end of the intermediate shaft.
The hammer will generally have a hammer housing with a hollow cylindrical spindle mounted within it and an air cushioning hammering mechanism mounted within the spindle. The hammering mechanism may include a piston, reciprocatingly mounted within the spindle and the wobble drive arrangement may reciprocatingly drive the spindle.
An embodiment of a hammer according to the present invention will now be described by way of example, with reference to the accompanying drawings in which:
The rotary hammer has a forward portion which is shown in FIG. 1 and a rearward portion incorporating a motor and a rear handle, in the conventional way. The handle may be of the pistol grip or D-handle type. The handle portion incorporates a trigger switch for actuating the electric motor, which motor is formed at the forward end of its armature shaft with a pinion (2). The pinion (2) of the motor rotatingly drives an intermediate shaft (6) via a gear (8) which gear is press fit onto the rearward end of the intermediate shaft (6). The intermediate shaft is mounted within a metal rearward housing part (10) of the hammer, so that it can rotate about it longitudinal axis. The intermediate shaft is mounted in the housing part (10) via a rearward bearing (9) which is press fitted onto the rearward end of the intermediate shaft and is fitted into a receiving recess (11) of the housing part (10). In the FIG. 1 arrangement the longitudinal axis of the motor is parallel with the longitudinal axis of the hollow cylindrical spindle (4) of the hammer. Alternatively, the motor could be aligned with its axis perpendicular to the axis of the spindle (4), in which case a bevel pinion would be formed at the end of the armature shaft of the motor, to mesh with a bevel gear press fit on the intermediate shaft (6) replacing the gear (8).